Coating composition and plastic articles coated therewith

ABSTRACT

An acrylic based terpolymer coating composition, adapted for use in coating polyolefin films, comprising an interpolymer of (a) from about 2 to about 15 parts by weight of an Alpha - Beta monoethylenically unsaturated carboxylic acid and (b) from about 85 to about 98 parts by weight of neutral monomer esters comprising an alkyl acrylate ester and an alkyl methacrylate ester.

United States Patent [191 Steiner 1 COATING COMPOSITION AND PLASTICARTICLES COATED THEREWITH [75] Inventor: Robert H. Steiner, Rochester,NY.

[73] Assignee: Mobil Oil Corporation, New York,

[22] Filed: July 2, 1971 [21] Appl. No.: 159,532

Related US. Application Data [63] Continuation-impart of Ser. No.561,367, June 29,

1966, abandoned.

[52] US. Cl.ll7/122 I-I, 117/1388 E, 117/161 UZ,

[51] Int. Cl. C08j l/40, C08f 45/52 [58] Field of Search 117/1388 E, 161UZ; 260/28.5 R, 29.6 A0, 80.8, 80.81

[56] References Cited UNITED STATES PATENTS 3,205,077 9/1965 Hammond117/1388 E [451 Aug. 21, 1973 3,297,477 1/1967 Barkis et al 260/28.53,205,077 9/1965 Hammond... 117/1388 E 3,248,356 4/1956 Snyder 260/8083,297,477 1/1967 Barkis et a1... 260/285 3,318,721 5/1967 Linburg117/1388 E 3,412,059 11/1968 Shakelmeyer -et a1. 260/285 PrimaryExaminer-Morris Liebman Assistant Examiner-S. L. Fox Art0rney-Oswa1d G.Hayes [57] ABSTRACT 2 Claims, No Drawings COATING COMPOSITION ANDPLASTIC ARTICLES COATED THEREWITI-I CROSS REFERENCES TO RELATEDAPPLICATIONS This application is a continuation-in-part of applicationSer. No. 561,367, filed June 29, 1966, now abandoned.

BACKGROUND OF THE INVENTION films such as polyethylene, polypropylene,polybutene, 1

and the like, whereby certain properties of such coated films areimproved. Specifically, uncoated polyolefin films such as polypropylenehave very high heat sealing temperatures,and an extremely narrow heatseal range, and especially in the case of oriented polypropylene, theyexhibit a tendency to disorient and tear when such sealing temperaturesare applied to the surface thereof. The coating composition of thepresent invention when applied to a substrate film such aspolypropylene, for example, substantially lowers the minimum heat sealtemperature of said film as well as substantially broadening the heatseal range of such a film product. Additionally, the present coatingcompositions impart increased stiffness or handle properties to thefilm, good hotslip characteristics, and facilitate the formation ofpeelable heat seals which permit opening of a package overwrapped withthe coated film material of this invention without tearing or destroyingthe wrapper.

2. Description of the Prior Art Typical heat sealing coatings which havebeen used in the past and disclosed in the prior art have been materialssuch as paraffin waxes and the like which are applied to substrates suchas paper, for example. However, paraffin wax is susceptible to blockingwhen a certain amount of pressure is applied and also subject toblocking under relatively warm and humid weather conditions. Attemptshave been made to produce coatings for thermoplastic film substratesemploying various hydrocarbon resins and-mixtures of resins and thelike'to provide, for example, improved heat seal properties, but in manyinstances such polymeric coatings have had other deleterious effects onthe final coated film product such as resulting in the coated filmexhibiting poor blocking characteristics, poor optical properties, poorheat stability and poor aging characteristics. Further, the polymerresin coating compositions of the prior art generally havecharacteristically low temperature softening points, which additionallycontributes to their poor blocking characteristics.

There has been a need for a coating composition which would not onlyimprove the heat seal characteristics of thermoplastic films, but wouldresult in a coated film product having low blocking characteristics,improve or at least have no adverse effects on the optical properties ofthe film such as gloss and clarity, improve the hotslip (i.e., theability of the film to slide across a heated surface), and improve thestiffness characteristics of the film thereby allowing ease of handlingand processability in automatic packaging equipment.

SUMMARY OF THE INVENTION In accordance with the present invention,resinous compositions are provided which may be employed inv coatingpolyolefin substrates, such as oriented polypropylene for example, tolower the heat seal temperature thereof while also increasing the heatseal temperature range. The compositions of the present inventioncontain as a film forming component a resin consisting essentially of aninterpolymer of (a) from about 2 to about 15 parts, and preferably fromabout 2.5 to about 6 parts by weight of an 01-3 monoethylenicallyunsaturated carboxylic acid selected from the group consisting ofacrylic acid, methacrylic acid, and mixtures 5 thereof, and (b) fromabout to about 98 and preferably from about 94 to about 97.5 parts byweight of neutral monomer esters, said neutral monomer esters preferablycomprising (1) methyl acrylate or ethyl acrylate and (2) methylmethacrylate. The interpolymer compositions of the present invention arefurther characterized by preferably comprising from about 30 percent toabout 55 percent by weight of methyl methacrylate when said alkylacrylate is methyl acrylate, and from about 52.5 percent to about 69percent by weight of methyl rnethacrylate when said alkyl acrylate isethyl acrylate.

DESCRIPTION OF SPECIFIC EMBODIMENTS The coating compositions of thepresent invention when applied to a suitable substrate film, such asoriented polypropylene for example, give coatings which possess hithertounavailable properties such as improving the heat seal properties of thefilm while simultaneously improving the blocking characteristics,hotslip properties, stiffness, and optical properties of the finalcoated film product.

The coating resins of the present invention when'applied to the surfaceof a film substrate exhibit relatively high temperature softeningpoints, i.e., on the order of about 170 F. and above. Accordingly, whenthe coated films for example in roll form are stored over prolongedperiods of time it has been found that under normal film storageconditions the overlying film layers exhibit little or no tendency toblock due to softening of the coating. This has been a particularlytroublesome prob- [em with many .prior art resinous coatings forthermoplastic films and has now been eliminated by employ ment of thenovel compositions of the present invention.

The present invention embodies a thermoplastic article, and particularlya polyolefin film such as polyethylene or polypropylene substrate, whichis coated on at least one surface thereof with a thin heat sealablepolymer film. The film is preferably initially pretreated to promotegood adhesion of the applied polymeric coating. The treated film is thencoated on at least one side with a terpolymer composition, preferablytogether with one or more other materials and including a finely dividedinorganic material.

In order for a coating resin to meet necessary commercial requirementssuch as for example being heat sealable at as low a temperature aspossible while exhibiting non-blocking characteristics at storageconditions which may be as high as l 1.0 E, it has been found that theglass transition temperature (Tg) of the resin coating should be in therange of from about 100 to about F. The Tg may be defined as the temperature at which a polymer changes from a glassy, brittle solid to a veryhigh viscosity liquid [Bueche, Physical Properties of Polymers,lnterscience Publishers, 1962]. At temperatures below or for that mattereven slightly above the Tg, polymers exhibit such great resistance toviscous flow that sealing does not take place, irregardless of appliedpressures or how long the polymer surfaces are left in contact with eachother.

Another requirement of a coating resin which is to be applied by wettechniques, as contrasted to hot melt techniques, is that it be solubleor dispersible in volatile solvents to give low viscosity, high solidscontent solutions or dispersions. For obvious commercial reasons, thesolvent should be readily available and inexpensive, with waterrepresenting the ultimate goal. Many coatings are applied as dispersionsof polymers in water, commonly called latices. However, the applicationof coatings from the latex form has several disadvantages. First, eventhe finest latex particles are massive in comparison to the ultimatemolecular size, containing many millions of resin molecules. Thisprevents the intimate blending of compounding ingredients which may bedesired in order to achieve certain properties. Second, most laticescontain very large amounts of surface active agents in order to maintainparticle dispersion. Those surfactants can be detrimental to the desiredproperties of the coating material such as adhesion, optical clarity,etc. On the other hand, truly water soluble polymers such as polyvinylalcohol are not desirable as coatings because of their tendency toabsorb moisture from the air at conditions of high relative humidity andbecome sticky. It is known that polymers containing pendant carboxylicacid groupings are soluble in water containing sufficient amounts of abase such as ammonia to neutralize the acid. The amount of acid requiredin a polymer for ammonia water solubility is dependent upon the natureof the other monomer units, but generally is in the range of from about2 to about 15 percent by weight. A coating of a resin of this typeapplied from ammonia water solution becomes water insoluble on dryingbecause of the volatilization of the solubilizing ammonia.

Finally, a heat scalable coating resin should have a sufficiently lowmolecular weight in order to exhibit sufficient viscous flow attemperatures moderately above the Tg to give a good seal. Also, lowmolecular weight is desirable to result in ammonia water solutions oflow viscosity.

In accordance with one aspect of the present invention, it has beenfound that the aforediscussed desirable properties of a heat scalablecoating resin may be achieved by controlled synthesis of themultipolymers of the present invention. 5

The novel multipolymers possessing the desired properties of Tg, acidcontent, and molecular weight may be produced in accord with the presentinvention by the proper selection and interpolymerization of thefollowing types of compounds, in the presence of a suitable chaintransfer agent such as for example mercaptans or halogenatedhydrocarbons:

A. A high Tg monomer;

B. A low Tg monomer; and

C. Acid containing monomers.

Examples of high Tg monomers which may be employed include ethylmethacrylate, methyl methacrylate and others.

Examples of low Tg monomers which may be employed include, for example,lower alkyl acrylates such as methyl, ethyl or butyl acrylates.

Examples of acid monomers which may be employed include, for example,acrylic acid, methacrylic acid, maleic acid, crotonic acid and mixturesthereof.

The polymerization reaction may be advantageously carried out by addingthe mixed monomers incrementally during the reaction in order to attaina more nearly homogeneous distribution of monomers in the multipolymermolecules.

The relative proportions of monomers which may be employed to producethe novel multipolymer coating compositions of the present invention mayvary and include between about 2 percent and about 15 percent, andpreferably from about 2 k percent to about 6 percent of an 01-13unsaturated carboxylic acid or mixtures thereof, and from about 85percent to about 98 percent, and preferably from about 94 percent toabout 97.5 percent by weight of the neutral ester monomers, saidmonomers having been interpolymerized utilizing known polymerizationtechniques, such as, for example, emulsion polymerization.

Thus, the present invention embodies, for example, terpolymers that maybe prepared by terpolymerizing ethylenically unsaturated monomersincluding between 2 percent and 15 percent by weight, and preferablyfrom about 2 A percent to about 6 percent by weight, of an 01-3unsaturated carboxylic acid and preferably acrylic or methacrylic acidand mixtures thereof; 85 percent to 98 percent, and preferably 94percent to 97.5 percent, by weight of neutral monomer esters comprising(a) an alkyl acrylate ester such as methyl, ethyl or butyl acrylate and(b) alkyl methacrylate esters such as methyl-methacrylate or ethylmethacrylate, for example. The monomer components are employed in aratio such that the alkyl methacrylate monomer is present in an amountof at least 10 percent by weight of the total terpolymer compositon andpreferably from about 20 to about percent by weight, and the alkylacrylate monomer component in amounts of at least 10 percent by weightof the total coating composition, and preferably from about 80 to about20 percent by weight.

In general, the uncoated substrate films employed in the practice of thepresentinvention are usually from 0.2 to up to 5 mils in thickness andpreferably from about 0.5 to 1.5 mils.

Before applying the coating composition to the appropriate substrate,the surface of the substrate film is treated to insure that the coatingwill be strongly adherent to the film thereby eliminating thepossibility of the coating peeling or being stripped from the film. Thistreatment may be accomplished by employing known prior art techniquessuch as, for example, film chlorination, i.e., exposure of the film togaseous chlorine, treatment with oxidizing agents such as chromic acid,hot air or steam treatment, flame treatment and the like. Although anyof these techniques may be effectively employed to pretreat the filmsurface, a particularly desirable method of treatment has been found tobe the so called electronic treatment method which comprises exposingthe film surface to a high voltage corona discharge while passing thefilm between a pair of spaced electrodes. After electronic treatment ofthe substrate film surface it may be coated with the coating compositionof the present invention which coating will then exhibit a tendency tomore strongly adhere to the treated film surface.

In applications where even greater coating-to-film adherence is desired,i.e. greater than that resulting from treatment of the film surface byany of the aforediscussed methods, an intermediate primer coating may beemployed to increase the adherence of the coating composition of thepresent invention to the substrate film. In that case the film is firsttreated by one of the foregoing methods, electronic treatment being apreferred method, to provide increased active adhesive sites thereon(thereby promoting primer adhesion) and to the thus treated film surfacethere is subsequently applied a continuous coating of a primer material.Such primer materials are well known in the prior art and for exampleinclude titanates and poly- (ethylene imine). A particularly effectiveprimer coating for purposes of the present invention has been found tobe poly(ethylene imine). The imine primer provides an overall adhesivelyactive surface for thorough and secure bonding with the subsequentlyapplied coating composition of this invention. The primer is applied tothe electronically treated basefilm by conventional solution coatingmeans such as mating roller application for example. It has been foundthat an effective coating solution concentration of the poly(ethyleneimine) applied from either aqueous or organic solvent media such asethanol, for example, is a solution comprising about 0.5 percent byweight of the poly- (ethylene imine).

It is possible to add the coating compositions of the present inventiononto the surface of the treated film substrate from a non-aqueoussolution of the composition using, for example, various organic solventssuch as alcohols, ketones, esters, etc. However, since the coatingcompositions of the present invention may, as stated hereinafter,contain colloidal inorganic materials and since such materials aredifficult to keep well dispersed in organic solvents, it is preferablethat the coating compositions of the present invention be applied fromaqueous media and preferably from. an alkaline aqueous solution thereof.

The solution of terpolymer, preferably in an alkaline aqueous solutionsuch as an ammoniacal solution, is applied to the treated surface of afilm material in any convenient and known manner, such as by gravurecoating, roll coating, dipping, spraying etc. The excess aqueoussolution may be removed by squeeze rolls, doctor knives, etc. Thecoating composition should be applied in such amount that there will bedeposited upon drying, a smooth evenly distributed layerof from 0.02 to0.04 mil thickness which, expressed otherwise, is equivalent to about0.4 to 0.8 grams per 1,000 sq. in. of film when both sides of the filmare being coated. In general, the thickness of applied coating is suchthat it is sufficient to impart the desired heat scalability andstiffness characteristics to the base film structure.

The coating on the film, as exemplified by use of an ammoniacal solutionof the terpolymer, is subsequently dried by hot air, radiant heat or byany other convenient means. Upon drying, ammonia is evolved leaving anon-water soluble, clear, adherent, glossy coated film useful, forexample, as a packaging film.

It is also an embodiment in the practice of this invention toincorporate a suitable component to the coating composition to imparthot slip," that is, satisfactory slip properties when the wrappingmaterial or partially wrapped package passes in contact with the heatsealing portions of wrapping apparatus such as heated platens, etc. Itis usually defined quantitatively as the coefficient of friction at thetemperature and pressure used.

In order to produce a coated wrapping material having the abovecharacteristics there is applied to the film a composition made up ofthe terpolymer component as hereinbefore described as the film formingand heat sealing agent together with a solid, finely divided, waterinsoluble, inorganic material such as colloidal silica, to function as ahot slip agent. Other finely divided inorganic materials which can beused to enhance hot slip properties include such water insoluble solidsas diatomaceous earth, calcium silicate, bentonite, and finely dividedclays. In order to function most efficiently, it is desirable that thisfinely divided inorganic material have a particle size between 10 and200 millimicrons, an alkali stabilized silica dispersion being thepreferred material for use.

While the amounts of each material required for producing the optimumhot slip properties may vary de pending on the specific material used,the coating compositions, and other variables of composition andprocess, it is preferred to use from 30 to 60 percent by weight (basedon the terpolymer) of the slip agent and preferably from about 35percent to about 45 percent by weight.

Blocking is the tendency of film to adhere to itself when two or moresurfaces of the film are held pressed together, for example when sheetsor mill rolls of the film are stacked in storage. It is more pronouncedat e1?- evated temperatures and high :relative humidities. Under normalstorage conditions, the maximum temperatures encountered will be between100 and 110 F. and the relative humidity may run as high as 90400percent. It is desirable that under these conditions the coated filmwill not stick to tiself, itself, in other words, that it be resistantto blocking. Otherwise, when the film is stored in rolled form on cores,for example, the layers will stick together and the film cannot readilybe unwound for use.

Anti-blocking materials which may be used include finely divided waxesand wax-like materials which melt at temperatures above themaximumtemperatures encountered in thestorage of the film and are not solublein the terpolymer at these temperatures. Specific examples are naturalwaxes such as paraffin wax, microcrystalline wax, beeswax, carnauba wax,japan wax, montan wax, etc., and synthetic waxes such as hydrogenatedcastor oil, chlorinated hydrocarbon waxes, long chain fatty acid amides,etc.

In addition to functioning as anti-blocking materials theabove-described wax materials when incorporated into the coatingcompositions of the present invention also function to improve thecold-slip properties of the films coated therewith, i.e., the ability ofa film to satisfactorily slide across surfaces at about roomtemperatures.

A particular type of thermoplastic film which can be advantageouslycoated with the coating compositions of this invention is molecularlyoriented, isotactic polypropylene. After extrusion of the basepolypropylene film utilizing conventional extrusion techniques the filmis heated and molecularly oriented by stretchingit in both alongitudinal and transverse direction. The resultant oriented filmexhibits greatly improved tensile and stiffness properties. However, itis difficult to heat seal by conventional techniques because at therequisite sealing temperature, i.e., on the order of about 350 F., filmdisorientation and shrinkage occur which results in the film rupturingand tearing apart. However, when such oriented films are subjected tosurface treatment methods as hereinbefore described and subsequentlycoated with the present novel coating compositions they can then besealed at temperatures sufficiently low to prevent shrinkage of thesubstrate, i.e., the oriented polypropylene film.

As hereinbefore noted standard polymerization techniques may be employedto produce the terpolymer coating compositions of the present inventionsuch as for example solution, bulk or emulsion polymerization. However,the preferred polymerization technique for purposes of the presentinvention and as set forth in the following Example is an emulsionpolymerization systern.

EXAMPLE I A reaction vessel was charged with l.2 liters of watercontaining 3.0 grams ofa commercially available emulsifier identified asGafac RE-6l0, a mixture of phosphoric acid esters; and 1.8 grams ofammonium persulfate as a polymerization catalyst. The reaction vesselwas then heated to a temperature of approximately 80 C. with stirring.The following materials were mixed and added incrementally with stirringover a period of 3 hours:

a. 216 grams of methyl methacrylate b. 366 grams of methyl acrylate c.18 grams of methacrylic acid and d. 2.2 grams of ethyl mercaptoacetateas a molecular weight regulator.

Following completion of the monomer addition the reaction vessel wasmaintained at the reaction temperature of 80 C. for an additional 30minutes. Upon termination of the reaction the product contained in thereaction consisted of a latex comprising 33 percent solids, i.e., 1 partterpolymer resin to two parts water. While still at a temperature of 80C. the latex reaction product was diluted with 1.2 liters of watercontaining dissolved therein 21.2 grams of ammonia. The mixture wasstirred for 1 hour at 60 to 70 C. and then allowed to cool to roomtemperature. The product was an ammoniacal aqueous solution of a methylmethacrylate/- methyl acrylate/methacrylic acid terpolymer with aviscosity of 20 cps (at 25 C.) and containing 20 percent terpolymerresin and 600 percent of the theoretical amount of ammonia required toneutralize the acid groups of the terpolymer. The dried polymer had anintrinsic viscosity of 0.28 and an acid number of 20.

To the ammoniacal aqueous solution of terpolymer was added (a) 40 parts(per 100 parts of terpolymer resin) of an aqueous dispersion (30 percentsolids) of an alkaline stabilized colloidal silica, identified by thetrade-name Syton; and (b) parts (per 100 parts of terpolymer resin) ofan aqueous dispersion (l 1 percent solids) of Camauba wax, resulting ina dispersion of wax and silica in the aqueous ammoniacal solution of theterpolymer composition.

EXAMPLE I] The procedure and conditions employed for theinterpolymerization and coating preparation used in Example I werefollowed with the exception that the monomer charge comprised thefollowing monomer components:

Methyl methacrylate 330 grams Ethyl acrylate 252 grams Methacrylic acid18 grams EXAMPLE Ill The procedure and conditions employed for theinterpolymerization and coating preparation used in Example l werefollowed with the exception that the monomer charge comprised thefollowing monomer components:

Methyl methacrylate 396 grams Butyl acrylate 186 grams Methacrylic acid18 grams EXAMPLE IV The procedure and conditions employed for theinterpolymerization and coating preparation used in Example I werefollowed with the exception that the monomer charge comprised thefollowing monomer components:

Methyl methacrylate 177 grams Methyl acrylate 64.5 grams Methacrylicacid 24 grams Acrylic acid 12 grams Each of the coating solutionsprepared in accordance with the foregoing examples were coated onto thesurface of biaxially oriented polypropylene film samples approximately0.7 mils thick. The film was produced from polypropylene resinidentified as Eastman Tenite 423DF, a non-slip polypropylene having ahigh isotactic content and a melt index of 4.5. The film, afterextrusion, was biaxially oriented utilizing techniques hereinbeforediscussed. The coatings were applied utilizing standard gravure coatingapparatus and techniques. Before coating, the film had been treated asaforedescribed by subjecting both surfaces thereof to electronictreatment and priming the electronically treated surfaces with apolyethylene imine solution consiting of 0.5 percent by weight ofpoly(ethylene imine) dissolved in a mixture of percent water and 15percent ethanol. The total coating weight on the oriented, treated,primed film surface after drying the film was approximately 0.6 grams/1,000 in. of film, both sides of the film having been coated.

The coated films were subsequently subjected to a variety of tests, theresults of which are reflected by the data contained in the followingtable. For comparison purposes a sample of uncoated orientedpolypropylene film was subjected to the same testing procedure and theresults thereof are also reported in Table l.

TABLE I Uncoated balanced Coated balanced oriented polypropylene tlimoriented polypropylene Example Example Example Example film I coating IIcoating III coating IV coating Gage, mils 0.83 0.90 0.88 0.01 0.86.Tensile strength, lbs/sq. in 20,000 25,000 25,500 24000 27,000. Tensileimpact strength, ft.-lh./cu. ln.. 1,400 1,300. Elongation at break,percent. 70 7 65 6O 05. Tensile modulus, lbs/sq. in 415,000 430,000.Coelliclent of friction..... 0.50 0.20. Gloss, Gardner (45 angl 00. 88.Haze, Gardner, percent 1. Minimum heat seal temperature, 1 345.. Heatseal strength", grains/inch Heat seal range, F l0 70 70.... 70 70.Blocking resistance Good Excellent... Good Fair Good. Hot slip Extremelypoor ..d0 ..do Good Fair.

Temperature at which a 75 g./inch seal is obtained at 2 seconds dwelltime; 100 g./sq. in. pressure.

" Sealed at 230 F.; 2 seconds; 100 g./in. pressure.

Thus, as apparent from the data contained in the foregoing table, theoriented polypropylene film sample coated with the polymer coatingcomposition of the present invention exhibits excellent seal strength,75 grams/inch being satisfactory for most commercial applications atrelatively low temperatures whereas the uncoated sample failed to sealat such temperatures.

The blocking resistance of the coated film at 100 F. and 90 percentrelative humidity was excellent. The coated film also exhibitedexcellent hot slip properties at the sealing element surfacetemperatures normally encountered in commercial wrapping equipment.

The cold slip properties of the coated film are improved as reflected bythe lowered coefficient of friction indicated in Table 1.

An additional advantage derived from the employment of the present novelcoatings is the increased seal range obtained, i.e., range oftemperature over which satisfactory seals may be made without burningthrough or otherwise destroying the film. For example, the coated filmsample prepared with the coating produced in accord with Example 1exhibited satisfactory heat sealing at temperatures as low as 210 F. andwere scalable at temperatures as high as 280 F. and higher without burnthrough of the substrate film occurring. Conversely, a similar sample oforiented polypropylene film without the present coating could only besealed at temperatures on the order of 350 F. i 5 F. Below thistemperature range, no seal occurred and above it the film ruptured andtore.

it has been found in accordance with the present invention that theportion of monomer components in the present composition in order toachieve a satisfactory coating for application to polyolcfin filmsubstrates must be maintained with certain specific limits. in thefollowing Tables ll, IV, and V, a series of terpolymers were preparedwith varying monomer concentrations and applied from a coating solutiononto the surface of a biaxially oriented polypropylene film substrate.

In Table 1 a series of terpolymers of methyl methacrylate, methylacrylate and methacrylic acid was prepared in which the Tg was variedfrom 55 to 150 F. by varying the ratio of MMA (methyl methacrylate) andMA (methyl acrylate). The Tgs were calculated by a well-knownmathematical procedure. (See, for exampie, T. E. Nielsen, MechanicalProperties of Polymers, Reinhold Publishing Co., 1962, pp. 22-27.)Sufficient chain transfer agent was incorporated in each polymerizationrecipe so that the resultant polymers had intrinsic viscosities in therange of 0.20 to 0.30. An MAA (methacrylic acid) content of 3.25 percentwas used in each case. The terpolymers were solubilized by adding anamount of ammonia equal to two times the amount required to neutralizethe polymeric acid content and sufficient water to produce a 22 percentsolids solution. The pH of these solutions was about 10 to I05 A coatingsolution was prepared from each resin solution by adding an aqueousdispersion of carnauba wax having an average particle size ofmillimicrons and 40 parts (dry weight) of a colloidal silica dispersionhaving an average particle size of 20 millimicrons per 100 parts (dryweight) of resin. The mixture was ap plied to one side of an orientedpolypropylene film having an average thickness of 0.75 mils by astandard gravure roll coating technique, the film having been previouslysubjected to a standard pretreatment to improve coating adhesion, namelya corona discharge treatment followed by coating with a very thin primercoat of polymerized ethylene imine. The wet coating was dried in a hotair oven at a temperature of about C. An average dry coating weight ofabout 0.6 gram/1,000 square inches of film was applied. The films thusobtained were tested for blocking, low pressure heat seal strength, andfilm-tofilm sliding cocfficient of friction. Practical experience hasshown commercially useful film should have a blocking value of not morethan 5 grams/inch, low pressure heat seal strengths of at leastgrams/inch at 230 F. sealing temperature and at least 150 grams/inch at250 F., and a coefficient of friction of less than 0.35. A study of thetest data presented in Table l reveals that coatings based onterpolymers with a Tg of less than about 100 F. are unsatisfac tory inregard to at least one of these criteria, even when a relatively largeamount (12 phr.) of wax is added. On the other hand, coatings based onterpolymers having a Tg greater than about F. are unsatisfactory even atreduced wax levels.

Similar terpolymers may be produced using ethyl acrylate as the low Tgmonomer rather than the methyl ester. Table III shows the Tg values ofterpolymers containing ethyl acrylate as the alkyl acrylate monomercomponent of the terpolymer composition.

TABLE II Film properties Polymer composl Coating tlon, percent Tgformulation 1 Block- Heat seal, g./in. C.O.F.

Ex. No. MMA MA MAA F. Wax SiO: g./in. 230 F. 250 F. slip slip 1 96. 753. 25 55 12 40 12 3 23 2 83. 3. 25 75 12 7 220 0. 40 5 3 3. 25 12 40 6.2 160 250 0.35 4 4 04 3. 25 103 12 40 4. 2 210 320 0. 33 2 5 .75 3. 25112 12 40 0.4 180 0.20 1 6 75 3. 25 112 8 40 1.0 170 240 0.23 l 7 53 3.25 8 40 0 150 210 0 25 1 8 75 3. 25 8 40 0 B0 200 0. 17 1 0. 75 3. 25130 6 40 O. 2 120 250 0. 29 1 1 42 3. 25 8 40 0 40 180 0. 27 l 1 42 3.25 140 6 40 0 100 210 0.33 l 1 75 3. 25 8 40 0 15 90 0.32 1 75 3. 25 1506 40 0 70 140 0. 38 1 1 All polymers had intrinsic viscosities in rangeof 0.24-0.28.

1 Carnauba wax dispersion, parts per 100 parts resin (dry basis).Carnauba silica dispersion, parts per 100 parts resin (dry basis) Peelstrength of pressure, 24 hours.

film stores (coating in contact with coating) at 100 F. 90% relativehumidity, l 1b./in.'

l Peel strength of film sealed under 100 gmsJinJ pressure, 2 secondstime, heat from one side only.

ll Film to film coeillcient of friction.

Hot slip rated quantitatively at 270 F.: l=excollent; 2=go0d; 3=fair;4=poor; 5=very poor.

TABLE [II MMA EA MAA Calculates 50 46.75% 3.25% 95F. 52.5 44.25 3.25IOO'F. 54 42.75 3.25 103F. 57.5 39.25 3.25 112F. 60.7 35.75 3.25 120F.64.6 32.15 3.25 130F. 69.2 27.55 3.25 104F. 73.0 23.75 3.25

colloidal silica (dry basis) and coated on oriented polypropylene filmas described in a previous paragraph. The test data presented in TableIV indicate that at least about 2.5 percent MAA is required to produce aterpolymer with a high degree of ammonia solubility and a desirablebalance of film properties. When the MAA content is higher than about 6percent, heat seal strengths at'low temperatures (230 F) are lower than30 desired.

TABLE IV Hoiutiou proportion Film proprrtleu limit maria, g.tlomprmitlou, percent Vl'moulty, llol. Blocking, MMA MA MAA (Jlnrlty11m. slip gun/in. 230" i 250' i". i. i".

42. 5 57.5 0 Milky ii 4 2.1 80 100 l. 38 41 57.5 1.5 (l0.. 5.5 4 1.2 140100 0.35 i0.5 57. 5 2.0 Very hazy. 12. 5 3 1.8 2.10 220 0.34 40. 0 57. 52. 5 II 18 2 2. ll 270 270 0. 3B 39. 5 57. 5 3.0 20 1 0. 7 190 250 0. 2839 57. 75 3. 25 22 l U. 4 220 0. 24 38. 25 57. 75 4. 0 25 l 0.3 140 0.2437 58 5. 0 v 35 1 0 13 0. 25 35 50 6. 0 55 2 1. 7 110 180 0. 24

I Brookfield viscosity of 22% solids solution.

To illustrate the importance of the acid monomer content of theterpolymers described in this invention, a series of coand terpolymersof MMA, MA and from 0 to 6 percent MAA was prepared. The ratios of theester monomers were adjusted so that all the polymers had calculated Tgsof about 112 F. Sufiicient chain transfer agent was used to regulate theintrinsic viscosity of each polymer to the range of 0.24-0.28. Theterpolymers were tested for ammonia-water solubility by stirring thelatexes with water and ammonia at 80 C. for one hour to produce adispersion or solution containing 22 percent solids and 200 percent ofthe amount of ammonia required to neutralize the acidic monomer. (in thefirst example which contained no acid monomer, sufficient ammonia wasadded to adjust the pH to the range of 1040.5.) Solubility of thepolymers was determined by visual examination of the haziness of thecooled solutions and measurement of the viscosity after 24 hoursstanding at room temperature. The terpolymer solutions were compoundedwith 8 phr. carnauba wax dispersion (dry basis) and 40 phr.

The importance of low molecular weight of the ter polymers described inthis invention was illustrated by preparing a series of polymerscontaining 3.25 percent MAA, 39 percent MMA and 57.75 percent MA (Tg 112 F.) in which the intrinsic viscosity was varied from 2.00 to 0.17 byvarying the amount of chain transfer agent (ethyl mercaptoacetate-EMA)employed during the emulison polymerization step used to produce theterpolymer compositions.

TABLE V Film properties Solution viscosity, cps. Heat seals, g./in.

cking,

g./in. 230 F. 250 F. 0.0.1:.

l Ethyl merca toacotate chain transfer agent; percent of monomer. IDetermined n dilute acetone solution.

3 Brookiield viscosity of aqueous solution containing 200% of the amountof ammonia required to neutralize the acid monomer.

Although the present invention has been described with preferredembodiments, it is to be understood that modifications and variationsmay be resorted to, without departing from the spirit and scope of thisinvention, as those skilled in the art will readily understand. Suchvariations and modifications are considered to be within the purview andscope of the appended claims.

I claim:

1. A polyolefin film substrate having a surface coating of a heatscalable composition consisting of an interpolymer as the film formingagent of (a) from about 2.5 to about 6 parts by weight of an a Bmonoethylenically unsaturated carboxylic acid selected from the groupconsisting of acrylic acid, methacrylic acid, and mixtures thereof, and(b) from about 97.5 to about 94 parts by weight of neutral monomeresters, said neutral monomer esters comprising (1) methyl acrylate orethyl acrylate and (2) methyl methacrylate, said interpolymer comprisingfrom about 30 percent to about 55 percent by weight of methylmethacrylate when said alkyl acrylate is methyl acrylate, and from about52.5 percent to about 69 percent by weight of methyl methacrylatewhensaid alkyl acrylate is ethyl acrylate; said interpolymer coating beingfurther characterized as containing (1) from about 30 percent to aboutpercent by weight based upon the total weight of said interpolymer, of ahot slip agent consisting of a finelydivided, water-insoluble, inorganicsolid selected from the group consisting of silica, diatomaceous earth,calcium silicate, bentonite and finely-divided clays, said inorganicsolid having a particle size between about 10 and about 200millimicrons, and (2) said interpolymer coating being furthercharacterized by containing a cold-slip, anti-blocking materialcomprising finelydivided wax.

2. A polyolefin film in accordance with claim 1 wherein said polyolefinis polypropylene and said inorganic solid is silica.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIONPATENT NO. 3,753,7 9 DATED August 21, 1973 lN\/ ENTOR(S) ROBERT H.STEINER It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Cover page, Item C01. 1, lines 6, 7 8c 8 [SEAL] Atlest:

RUTH C. MASON A [testing Offi "Continuation-in-part of Serial No.561,367, June 29, 1966, abandoned should be Continuation of Ser. No.881,626, December 2, 1969 now abandoned, which is a continuationin-partof -Ser. No. 561,367, filed June 29, 1966, now abandoned Signed andScaled this seventh Day Of October 1975 C. MARSHALL DANN' ommissr'rmerufParents and Trademarks

2. A polyolefin film in accordance with claim 1 wherein said polyolefinis polypropylene and said inorganic solid is silica.